1. Field of the Invention
The present invention relates to a laminate sheathed cable, more particularly, it relates to a laminate sheathed cable having a shielding tape or layer prepared by coating a metallic foil with a specific resin having a good adhesive property not only for the metallic foil but also polyethylene used as an outer jacketing or protective layer.
2. Description of the Prior Art
A resin used for lamination in laminate sheathed cables is required to have good processing and mechanical properties during production of the cable, for example, high abrasion resistance to tape forming apparatus, etc., and good adhesion for both metallic foil and a jacketing compound, such as polyethylene.
Aluminum is usually used for such a metallic foil, and the reason why the laminate resin is required to have good adhesion for the metallic foil and the polyethylene which is usually used as the jacketing layer is partially to improve the moisture resistance, that is, the laminate resin must serve to prevent moisture permeation as well as to improve the mechanical strength such as bending property, etc., in a unitized sheath (jacketing layer) by strongly laminating the metallic foil to the polyethylene jacketing layer and must also help to control the shrinkage of the sheath (a plastic sheath has stress therein at extrusion and thus shrinks due to the heat cycle upon exposure to the open air) by the metallic foil.
As the resin for the laminate, polyethylene has ordinarily been used, as shown in British Pat. No. 886,417, but polyethylene is lacking in bonding strength to the aluminum foil.
This defect of polyethylene is partially overcome by the invention described in U.S. Pat. No. 3,233,036 wherein a resin or polymer containing a carboxyl group is employed to improve the bonding strength to an aluminum foil, but the proposed resin has the defect that a sufficient bonding strength for polyethylene as the jacketing layer is not obtained.
An attempt to overcome the aforesaid two defects is also disclosed in U.S. Pat. No. 3,586,756, which teaches a so-called two-layer or multi-layer laminate tape, having at the side to be brought into contact with a metallic foil, such as aluminum foil, a layer of an ethylene copolymer having a carboxyl group capable of being chemically bonded to the metallic foil and, at the opposite side of the aforesaid ethylene copolymer, a layer of resin which does not have an effective bonding strength for the metallic foil as does the ethylene copolymer, but which has a higher bonding strength for the jacketing layer than the ethylene copolymer.
When a laminate tape of this kind is used the mechanical properties of the laminate sheathed cable are excellent, but since the laminate tape has a two-layer or multi-layer structure the production of the laminate tape is complicated and the production costs become high, which results in increasing the cost of the cable.